Heart rate measurement using blood pump impeller location

ABSTRACT

A method of determining a heart rate of a patient having an implanted blood pump including applying a voltage to a plurality of coils of a stator of the blood pump to produce an electromagnetic force to rotate a rotor in communication with the plurality of coils; displaying a waveform associated with a back electromotive force in the plurality of coils of the blood pump, the waveform being proportional to an axial position of the rotor relative to the stator; determining a time interval between a first alteration in the waveform relative to a baseline and a second alteration in the waveform relative to the baseline; and determining the heart rate of the patient based on the time interval.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Application Ser. No.62/607,478, filed Dec. 19, 2017, which is incorporated by reference inthe entirety.

FIELD

The present technology is generally related to determining heart ratemeasurements of patients having an implanted blood pump.

BACKGROUND

Mechanical Circulatory Support Devices (“MCSDs”) are commonly used toassist the pumping action of a failing heart. Typically, an MCSDincludes an implantable blood pump that is surgically implanted in apatient's body. The MCSD may include a housing with an inlet, an outlet,and a rotor mounted therein. The inlet is connected to a chamber of thepatient's heart, typically the left ventricle, whereas the outlet isconnected to an artery, such as the aorta. Rotation of the rotor drivesblood from the inlet towards the outlet and thus assists blood flow fromthe chamber of the heart into the artery. One exemplary MCSD is theMVAD® Pump. The MVAD® Pump is further discussed in U.S. Pat. Nos.8,007,254 and 9,561,313, the disclosures of which are incorporatedherein in the entirety. Unfortunately, determining a heart rate of apatient having an operating MCSD implanted within the patient's body maybe difficult, particularly when there is a non-linear relationshipbetween a blood flow rate through the blood pump and a motor current ofthe blood pump.

SUMMARY

The techniques of this disclosure generally relate to determining aheart rate of a patient having an implanted blood pump during operationof the blood pump.

In one aspect, the present disclosure provides a method of determining aheart rate of a patient having an implanted blood pump includingapplying a voltage to a plurality of coils of a stator of the blood pumpto produce an electromagnetic force to rotate a rotor in communicationwith the plurality of coils; displaying a waveform associated with aback electromotive force in the plurality of coils of the blood pump,the waveform being proportional to an axial position of the rotorrelative to the stator; determining a time interval between a firstalteration in the waveform relative to a baseline and a secondalteration in the waveform relative to the baseline; and determining theheart rate of the patient based on the determined time interval.

In another aspect, the disclosure provides the first alteration being afirst rise in the waveform relative to the baseline and the secondalteration being a second rise in the waveform relative to the baseline.

In another aspect, the disclosure provides recording one or more-timeintervals between one or more rises in the waveform relative to thebaseline and calculating the heart rate based on the time intervals.

In another aspect, the disclosure provides the baseline being an upperhysteresis band.

In another aspect, the disclosure provides the first alteration being afirst fall in the waveform relative to the baseline and the secondalteration being a second fall in the waveform relative to the baseline.

In another aspect, the disclosure provides recording one or more-timeintervals between one or more falls in the waveform relative to thebaseline and calculating the heart rate based on the one or more-timeintervals.

In another aspect, the disclosure provides the axial position of therotor relative to the stator being proportional to a thrust through theblood pump, and the thrust is proportional to a fluid flow through theblood pump.

In another aspect, the disclosure provides determining the heart rate ofthe patient in a presence of a non-linear relationship between the fluidflow through the blood pump and a motor voltage of the blood pump.

In one aspect, the present disclosure provides a method of determining aheart rate of a patient having an implanted blood pump includinggenerating a waveform representing a back electromotive force in one ormore coils of the blood pump during operation; detecting one or morealterations in the waveform relative to a baseline, the alterationsbeing one of the group consisting of a rise and a fall in the waveformrelative to the baseline; recording a time interval between at least apair of adjacent alterations of the alterations; and determining theheart rate of the patient based on the time interval.

In another aspect, the disclosure provides the blood pump including arotor and a stator in communication with the rotor, and the waveform isproportional to an axial position of the rotor relative to the stator.

In another aspect, the disclosure provides the axial position of therotor relative to the stator being proportional to a thrust through theblood pump, and the thrust is proportional to a fluid flow through theblood pump.

In another aspect, the disclosure provides determining the heart rate ofthe patient in a presence of a non-linear relationship between the fluidflow through the blood pump and a motor current of the blood pump.

In another aspect, the disclosure provides the time intervalcorresponding to a complete heartbeat of the patient.

In another aspect, the disclosure provides including correlating thetime interval to a predetermined figure.

In another aspect, the disclosure provides dividing the time interval bythe predetermined figure of sixty to determine a number of heart beatsper minute.

In another aspect, the disclosure provides the baseline being an upperhysteresis band, and the rise in the waveform includes a crossing of theupper hysteresis band.

In another aspect, the disclosure provides correlating the waveform to alower hysteresis band separate from the upper hysteresis band, andwherein the fall in the waveform includes a crossing of the lowerhysteresis band.

In another aspect, the disclosure provides calculating the heart rate ofthe patient based on a frequency analysis of the waveform.

In another aspect, the disclosure provides determining a variabilitywith respect to the determined heart rate of the patient over a selectduration.

In one aspect, the present disclosure provides a system for determininga heart rate of a patient including a control circuit in communicationwith an implantable blood pump including a rotor and a stator incommunication with the rotor, the control circuit including controlcircuitry configured to generate a waveform representing a backelectromotive force in a plurality of coils of the blood pump duringoperation, the waveform being proportional to an axial position of therotor relative to the stator; detect a plurality of alterations in thewaveform relative to a baseline, the plurality of alterations being oneof the group consisting of a rise and a fall in the waveform relative tothe baseline; record a plurality of time intervals between adjacentalterations of the plurality of alterations, each of the plurality oftime intervals corresponding to a complete heartbeat of the patient;correlate each of the plurality of time intervals to a predeterminedfigure; and determine the heart rate of the patient based on thecorrelated plurality of time intervals.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described in this disclosurewill be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram that illustrates a system including animplantable blood pump and a controller including a processor incommunication with the blood pump;

FIG. 2 is an exploded view that illustrates an exemplary blood pumpconstructed in accordance of the principles of the present application;

FIG. 3 is a graph that illustrates a waveform associated with a backelectromotive force in one or more coils of a rotor of the blood pumpshown in FIG. 1;

FIG. 4 is another graph that illustrates the waveform associated withthe back electromotive force in one or more coils of the rotor of theblood pump shown in FIG. 1; and

FIG. 5 is a flow diagram that illustrates a method of determining aheart rate of a patient having the blood pump implanted in the patientduring operation of the blood pump.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of system components andprocessing steps related to a method and system for determining a heartrate of a patient having an implanted blood pump. Accordingly, thesystem and method components have been represented where appropriate byconventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments of thepresent disclosure so as not to obscure the disclosure with details thatwill be readily apparent to those of ordinary skill in the art havingthe benefit of the description herein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the concepts described herein. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Referring now to the drawings in which like reference designators referto like elements there is shown in FIG. 1 a block diagram of anexemplary system 10 constructed in accordance with the principles of thepresent application and designated generally “10.” The system 10includes an implantable blood pump 12 in communication with a controller14. The blood pump 12 may be the MVAD® Pump or another mechanicalcirculatory support device fully or partially implanted within thepatient. The controller 14 includes a control circuit 16 having controlcircuitry for monitoring and controlling startup and subsequentoperation of a motor 18 implanted within the blood pump 12. Thecontroller 14 may also include a processor 20 having processingcircuitry, a memory 22, and an interface 24. The memory 22 storesinformation accessible by the processor 20 and processing circuitry,including instructions 26 executable by the processor 20 and/or data 28that may be retrieved, manipulated, and/or stored by the processor 20.

The blood pump 12 may be a continuous flow blood pump, such as, withoutlimitation, the MVAD® Pump referenced above, and may include a housinghaving a rotor therein. The system 10 and the blood pump 12 may be usedin conjunction with a method of determining a heart rate of a patienthaving the blood pump implanted with the patient's body based upon anaxial position of the rotor with respect to the housing, as discussed infurther detail below.

FIG. 2 is an exploded view of the blood pump 12 include a housing 30having an inlet cannula 32 and a rotor 34 such as an impeller, proximatethe inlet cannula 32 to impel the blood. The inlet cannula 32 includesan inner tube 36 formed from a non-magnetic material, such as a ceramic.The inner tube 36 includes an interior surface 38 defining a cylindricalbore 40 for receiving the rotor 34 therein. The inner tube 36 alsoincludes a cylindrical outer surface 42 surrounded by a stator 44 havingone or more coils 46. A voltage is applied to the coils 46 from a drivecircuit (not shown) to produce an electromagnetic force to rotate therotor 34. In particular, the electromagnetic force of the coils 46exhibits an electromagnetic field which interacts with a magnetic fieldof the rotor 34 to suspend the rotor 34 within the cylindrical bore 40and rotate the rotor 34. In addition to or in lieu of the magneticforces, the rotor 34 may be suspended within the housing 30 using one ormore hydrodynamic forces.

Rotation of the rotor 34 impels the blood along a fluid flow path froman upstream direction U to a downstream direction D through the innertube 36. The fluid flow path may be referred to as a blood flow path.Further details associated with rotary blood pumps are described in U.S.Pat. No. 8,007,254, the disclosure of which is incorporated herein byreference in the entirety. The blood pump 12 defines a housing axis “A”extending therethrough and along the fluid flow path from the upstreamto the downstream direction. The rotor 34 moves in an axial directionrelative to the housing 30 along the housing axis. When fluid, such asblood, passes through the blood pump 12, the fluid imparts a thrust onthe rotor 34 which causes the rotor 34 to move. A magnitude of thethrust is related to the fluid flow rate through the blood pump 12. Inother words, the axial position of the rotor 34 relative to the housing30 is proportional to the fluid flow rate through the blood pump 12,which is proportional to the thrust.

The patient's heart beat is determined by analyzing the axial positionof the rotor 34 relative to the housing 30, and particularly the stator44. For example, a back electromotive force (“BEMF”) is produced in thecoils 46 when the voltage is applied to the coils 46 to rotate the rotor34. In other words, the BEMF is the voltage induced in the coils 46 byrotating the rotor 34. The axial movement of the rotor 34 alters thealignment between the rotor 34 and the coils 46 which alters the BEMF.The slope of the BEMF is analyzed to derive the patient's heart beat. Inaddition to or in lieu of using the BEMF, a sensor (not shown) disposedwithin the housing 30 may be used to determine the axial position of therotor 34 relative to the stator 44.

FIG. 3 is a graph that illustrates an exemplary waveform 48 of the BEMFin a pulsatile flow system over approximately ten seconds at sixty beatsper minute. The term approximately includes a deviation within plus orminus five seconds. The control circuit 16 and the control circuitry(FIG. 1) are configured to generate the waveform 48. The waveform 48shows alterations in the BEMF signal's amplitude relative to a baseline50 over time. The alterations in the waveform 48 are detected and viewedand/or recorded to determine the patient's heart beat. For example, atime interval between adjacent pairs of rises and/or falls in thewaveform 48 relative to the baseline 50 represent a duration of anindividual heartbeat. In other words, the time interval is the time ittakes to complete a single complete heartbeat. The heartbeat iscorrelated to a predetermined figure to determine the patient's heartrate in beats per minute. For example, the predetermined figure may bethe number 60 with the time interval being divided by the number 60 tooutput the heart rate in beats per minute. The number of time intervalsused to determine the heart rate may vary. The heart rate may bedetermined regardless of a speed of the blood pump 12, such as whenthere is a non-linear relationship between the fluid flow through theblood pump 12 and the speed, which may occur in the MVAD® Pump.

In another configuration, the heart rate may be determined by performinga frequency analysis of the waveform 48. The time interval calculationsand/or the frequency analysis are performed using one or more algorithmsor other calculation methods. The waveform 48 may be displayed on amonitor of the controller 14 or a remote location, such as a remotelocation viewable by a clinician. The waveform 48 is provided forillustrative purposes as the duration and number of beats per minute mayvary in accordance with individual patients. The determined heart ratemay be used to derive additional parameters, such as the patient's heartrate variability over time, for clinical or other use. For example, thevariability with respect to the patient's heart rate may be determinedover weeks, months, and/or years to determine whether the patient'shealth condition is deteriorating.

FIG. 3 depicts a first alteration in the waveform 48 as a first rise 52in the waveform 48 relative to the baseline 50. The baseline 50 is anupper hysteresis band which is separate from a lower hysteresis band 54by a filter 56. The baseline 50 or the upper hysteresis band and thelower hysteresis band 54 are used to reduce the occurrence of faultytriggers in the rises, which may otherwise occur due to outside factors,such as noise. The rise in the waveform 48 refers to the waveform 48crossing the baseline 50. Once the first rise 52 is detected, a timerruns until a second rise 58 in the waveform 48 is detected relative tothe baseline 50 and the timer stops. A time interval, designated as an“n-n interval”, is recorded between the first rise 52 and the secondrise 58 and stored in the memory 22 (FIG. 1). The time interval betweenthe first rise 52 and the second rise 58 represents the time durationbetween individual heart beats.

FIG. 4 is a graph that illustrates a first alteration of the waveform 48as a first fall 60 in the waveform 48 relative to the baseline 50. Thefall in the waveform 48 refers to the waveform 48 crossing the lowerhysteresis band 54. Similar to the first rise 52 in the waveform 48(FIG. 3), when the first fall 60 is detected a timer runs until a secondfall 62 in the waveform 48 is detected relative to the baseline 50, atwhich time the timer stops. A time interval between the first fall 60and the second fall 62, such as the n-n interval, is recorded and storedin the memory 22. Two or more of the time intervals may be determinedand recorded to determine the average heart rate.

FIG. 5 is a flow chart depicting steps of an exemplary method 64 ofdetermining the heart rate of a patient having an implanted blood pump.The control circuit 16 and the control circuitry (FIG. 1) may beconfigured to execute the steps of the method. In one exemplaryconfiguration, the method begins with step 66 and proceeds to step 68 ofapplying a voltage to the coils 28 of the stator 44 of the blood pump 12to produce an electromagnetic force to rotate the rotor 34 incommunication with the coils 28. As mentioned above, the voltage isapplied through a drive circuit (not shown). At step 70, the methodincludes displaying the waveform 48 associated with the backelectromotive force in the coils 28 of the blood pump 12 with thewaveform 48 being proportional to an axial position of the rotor 34relative to the stator 44. The waveform 48 may be generated using thecontroller 14 and control circuit 16 (FIG. 1) and displayed on a monitorof the controller 14 (not shown) or at another remote location. At step72, the method 64 includes determining the time interval between thefirst alteration in the waveform 48 relative to the baseline 50 and asecond alteration in the waveform 48 relative to the baseline 50. Thefirst and second alterations are the rise and/or the fall with respectto the baseline 50. At step 74, the method 64 includes determining theheart rate of the patient based on the determined time interval asdiscussed in further detail above.

It should be understood that various aspects disclosed herein may becombined in different combinations than the combinations specificallypresented in the description and accompanying drawings. It should alsobe understood that, depending on the example, certain acts or events ofany of the processes or methods described herein may be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,all described acts or events may not be necessary to carry out thetechniques). In addition, while certain aspects of this disclosure aredescribed as being performed by a single module or unit for purposes ofclarity, it should be understood that the techniques of this disclosuremay be performed by a combination of units or modules associated with,for example, a medical device.

In one or more examples, the described techniques may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include non-transitorycomputer-readable media, which corresponds to a tangible medium such asdata storage media (e.g., RAM, ROM, EEPROM, flash memory, or any othermedium that can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor” as used herein may refer toany of the foregoing structure or any other physical structure suitablefor implementation of the described techniques. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

1-20 (canceled)
 21. A system comprising: an implantable blood pumpcomprising a rotor and a stator with a plurality of coils, wherein theimplantable blood pump is configured to pump blood from a chamber of aheart of a patient; and a controller comprising a memory and processingcircuitry configured to: generate a waveform representing a backelectromotive force in the plurality of coils during operation of theimplantable blood pump; detect a plurality of alterations in thewaveform relative to a baseline, the plurality of alterations includingone or both of rises and falls in the waveform relative to the baseline;record a time interval between at least a pair of adjacent alterationsof the plurality of alterations; determine a heart rate of the patientbased on the time interval; and output an indication of the heart rate.22. The system of claim 21, wherein the waveform is proportional to anaxial position of the rotor relative to the stator.
 23. The system ofclaim 22, wherein the axial position of the rotor relative to the statoris proportional to a thrust through the implantable blood pump, and thethrust is proportional to a fluid flow through the implantable bloodpump.
 24. The system of claim 21, wherein the processing circuitry isfurther configured to determine the heart rate of the patient in apresence of a non-linear relationship between a fluid flow through theimplantable blood pump and a motor current of the implantable bloodpump.
 25. The system of claim 21, wherein the time interval correspondsto a complete heartbeat of the patient.
 26. The system of claim 25,wherein the processing circuitry is further configured to correlate thetime interval to a predetermined figure to determine a number of heartbeats per minute.
 27. The system of claim 21, wherein the baselinecorresponds to an upper hysteresis band, and the processing circuitry isconfigured to detect a rise in the waveform in response to the waveformcrossing the upper hysteresis band.
 28. The system of claim 21, whereinthe baseline corresponds to a lower hysteresis band, and the processingcircuitry is configured to detect a fall in the waveform in response tothe waveform crossing the lower hysteresis band.
 29. The system of claim21, wherein the processing circuitry is further configured to determinethe heart rate of the patient based on a frequency analysis of thewaveform.
 30. The system of claim 21, wherein the processing circuitryis further configured to determine a variability with respect to thedetermined heart rate of the patient over a select duration.
 31. Adevice comprising: a memory; and processing circuitry configured to:generate a waveform representing a back electromotive force in aplurality of coils of a blood pump device during operation of the bloodpump device; detect a plurality of alterations in the waveform relativeto a baseline, the plurality of alterations including one or both ofrises and falls in the waveform relative to the baseline; record a timeinterval between at least a pair of adjacent alterations of theplurality of alterations; determine a heart rate of a patient based onthe time interval; and output an indication of the heart rate.
 32. Thedevice of claim 31, wherein the waveform is proportional to an axialposition of a rotor of the blood pump device relative to a stator of theblood pump device.
 33. The device of claim 31, wherein the processingcircuitry is further configured to: determine the heart rate of thepatient in a presence of a non-linear relationship between a fluid flowthrough the blood pump device and a motor current of the blood pumpdevice.
 34. The device of claim 31, wherein the time intervalcorresponds to a complete heartbeat of the patient.
 35. The device ofclaim 31, wherein the baseline corresponds to an upper hysteresis band,and the processing circuitry is configured to detect a rise in thewaveform in response to the waveform crossing the upper hysteresis band.36. The device of claim 31, wherein the baseline corresponds to a lowerhysteresis band, and the processing circuitry is configured to detect afall in the waveform in response to the waveform crossing the lowerhysteresis band.
 37. A method comprising: generating a waveformrepresenting a back electromotive force in a plurality of coils of ablood pump device during operation of the blood pump device; detecting aplurality of alterations in the waveform relative to a baseline, theplurality of alterations including one or both of rises and falls in thewaveform relative to the baseline; recording a time interval between atleast a pair of adjacent alterations of the plurality of alterations;determining a heart rate of a patient based on the time interval; andoutputting an indication of the heart rate.
 38. The method of claim 37,wherein the waveform is proportional to an axial position of a rotor ofthe blood pump device relative to a stator of the blood pump device. 39.The method of claim 37, further comprising determining the heart rate ofthe patient in a presence of a non-linear relationship between a fluidflow through the blood pump device and a motor current of the blood pumpdevice.
 40. The method of claim 37, wherein the time intervalcorresponds to a complete heartbeat of the patient.